I really loved this scene because Jax completely froze and didn't stop looking her way even after she left, he was frozen and lost in his thoughts while Pomni was left in a very awkward position because of the tension between those two oh i hate them
Jax assumed he knew the full truth of who Ragatha is as a person, he assumed that he could taunt her into becoming like him, as prideful as him. He most likely assumes everyone is like that.
This is how he talks about her
That is how anyone talks about someone they don't know on a deeper level but they still feel suspicious of or simply don't like. He assumes she's pretending all the time and that her kindness has no meaning. He assumes he knows her.
And when she apologized, when she admitted and even went back to her own mistake from earlier and mentioned it herself despite her pride being hurt (something he would not do about his own mistakes because of his pride and the persona he puts on)
When she did that she immediately shattered the perception and narrative he had built in his mind about her, that deep inside she was mean and everything she was was a farse. She actually faced her flaws and apologized and proved him wrong and he has no idea how to deal with that